This invention relates to a method and apparatus for servowriting a disk drive, in particular, a magnetic disk drive. More particularly, the method and apparatus may be used with a sealed head-disk assembly by employing an optical source to sense an optically detectable pattern formed previously on a rotating surface of the head-disk assembly, thereby eliminating the need to servowrite in a contamination controlled environment, and eliminating the need for a servowriter clock head assembly.
In the present art of manufacturing rotating disk magnetic data storage devices, referred to as disk drives, it is necessary to place accurate magnetic patterns, referred to as servo patterns, on the surface of one or more disks in the disk drive. These servo patterns are used during normal operation of the disk drive as position reference points in order to place the magnetic read and write heads of the disk drive at any particular radius of any disk so that data may be written to or read from the magnetically alterable surface of the disk. Typically these patterns also contain information describing the angular position of the disk as well as the radius so that magnetic data may be written to, or read from, precise geometrically defined areas of any disk in the disk drive. Ordinarily, these patterns are written on one or more of the disk surfaces in a disk drive by a machine referred as a servowriter. In order to write the accurate magnetic patterns on the disk, the servowriter uses an accurate clock signal as a reference for the placement of these patterns.
The accurate clock signal must maintain a precise geometric relationship with the rotating disk assembly while the servo patterns are being formed. In order to attain the necessary precision, it is a present practice to form the accurate clock on the surface of at least one of the disks in the disk drive. Typically, a separate magnetic head assembly, commonly referred to as a clock head assembly, which is part of the servowriter, forms this accurate clock. During clock pattern formation, the clock head assembly is typically moved to the outer radius of at least one of the disks in the disk drive. At this radial position the clock head assembly forms a magnetic clock pattern on at least one of the disks in the disk drive. After this clock pattern is formed, it is then sensed by the same clock head assembly or another clock head assembly for use as an accurate reference clock for forming servo patterns on the surface of one or more of the disks in the disk drive.
The present art for most disk drives requires that the disk and spindle assembly be kept very clean and free of contamination. Otherwise, the surface of the disks may be physically damaged, destroying the data storage capability of the disks. To prevent this contamination, the disk and spindle assembly of the disk drive is placed in a sealed enclosure during normal use. However, in order to use the clock head assembly to form and sense the accurate reference clock, an opening must be made in the sealed enclosure. Unfortunately, this opening permits contamination to enter the otherwise sealed disk and spindle assembly enclosure. Moreover, the clock head assembly itself may become contaminated and thereby transfer contamination through the opening and into the enclosure when it is moved into place near the disks. To reduce the risk of damage resulting from such contamination, the accurate clock pattern and the servo patterns are typically placed onto the disks in a contamination-controlled environment such as in a clean room or underneath a flow-hood. To further reduce contamination, the magnetic heads of the clock head assembly are regularly changed. The cost of buying and maintaining clean rooms is substantial as is the cost of suitable flow hoods. The cost of replacement magnetic heads for the clock head assembly is also substantial.
Accordingly, there is a need for a method and apparatus for sensing optically detectable patterns formed on the surfaces of the rotating members of a disk drive.
The present invention replaces the magnetic clock head assembly of a servowriter with an optical sensor which detects an optically detectable pattern on the surface of one of the magnetic disks or, for that matter, on the surface of any of the rotating members of the disk and spindle assembly of a disk drive. This optically detectable clock pattern is formed by optical light pulses which are focused on one or more of the aforementioned surfaces. This clock pattern formation is typically done at some prior step in the disk drive manufacturing process by a separate device designed for forming such optically detectable clock patterns. This pattern-forming device may also be advantageously used to form textured surface patterns on the disk surface which may be used to control the flying height of a head which flies over the disk. Additionally, this optically detectable clock pattern-forming device may be advantageously employed to form a textured surface pattern on a disk surface in order to control the friction characteristics between a head and disk when the head comes into contact with the disk.
The present invention is a method and apparatus for reading an optically formed clock pattern from the surface of one or more of the rotating members of a disk drive. An accurate clock is formed using a signal generated by an optical sensor which detects or reads the previously formed optically detectable clock pattern. The disk drive then uses this accurate clock to form servo patterns on one or more of the disks in a disk drive. The optical sensor of the present invention can remain outside of the disk and spindle enclosure of the disk drive and senses the optically detectable pattern by passing a light beam through an opening in the disk and spindle enclosure of the disk drive. This opening may optionally be covered with a transparent window. By sensing the clock pattern from outside the sealed enclosure the risk of damage from contamination is greatly reduced. As a result, the use of clean rooms and flow hoods becomes unnecessary for the formation of servo patterns on the disks of a disk drive. The monetary cost of buying and maintaining clean rooms and flow hoods and replacing magnetic heads for the servowriter clock head assembly can be reduced or eliminated.